1. Field of the Invention
The present invention relates to a recording sheet and a method of recording an image using such a recording sheet, and more particularly to a recording sheet which is resistant to water and free of ink blurring, and a method of recording an image using such a recording sheet.
2. Description of the Prior Art
Ink-jet recording processes produce ink droplets based on various principles in ink-jet printers and apply the generated ink droplets to a receptive layer on a recording sheet for thereby forming a printed image thereon. Ink-jet printers are widely used in the art because they are capable of producing clear printed images and are relatively inexpensive to manufacture.
According to the ink-jet recording processes, water-base inks are generally used for protection against being dried in the ink-jet printers. The water-base inks that are used are so-called dye inks which comprise water-soluble dyes. Recording sheets for use with such dye inks generally have a receptive layer that is mainly made of a water-absorbent or water-soluble resin for receiving water-base inks.
One known recording sheet of the type described above is disclosed in Japanese patent publication No. 5-33150, for example.
The disclosed recording sheet has a receptive sheet which comprises a light-transmissive layer containing a copolymer of acrylic acid and vinyl alcohol or its salt. Since the copolymer of acrylic acid and vinyl alcohol or its salt is highly absorbent of water, can dry quickly, and is highly capable of transmitting light therethrough, the disclosed recording sheet can record images with high resolution and high color densities when used with water-base inks containing water-soluble dyes.
Recently, ink-jet printers have been attracting much attention for use in business applications. For example, ink-jet printers are used to print images on large recording sheets such as of A0, A1 or like sizes for thereby producing advertising sheets or posters. Such applications demand high-quality printed images because clearly printed images attract observer's attention easily.
One problem with recording sheets for use with ink-jet printers is that they are liable to absorb humidity in the ambient air as they are highly water-absorbent. Therefore, when images printed on such recording sheets are displayed indoors or outdoors over a long period of time, the images tend to be subject to blurring or characters included in the printed images are apt to decay easily.
It is known that the ability of recording sheets to resist water and discoloration can be improved by adding a hardener to their receptive layer. The above publication states that a hardener can be added to the receptive layer of the disclosed recording sheet. When a hardener was actually added to the receptive layer of the disclosed recording sheet, however, the ability of the receptive layer to absorb water was lowered, resulting in ink blurring and ink absorption irregularities though the ability of the receptive layer to resist water was somewhat increased. Therefore, the recording sheet disclosed in the above publication needs to be improved if it is to be used for printed materials that will be displayed indoors or outdoors over a long period of time.
If printed images are required to be resistant to discoloration and water, then pigment inks comprising pigments that can be dispersed well into water are used to print images. However, the pigment inks are disadvantageous in that they cannot easily permeate into a receptive layer, as the pigments are not water-soluble. Therefore, when a pigment ink is applied to the receptive layer of a recording sheet, the pigment which does not permeate into the receptive layer remains on the surface of the receptive layer and spreads around the printed region, resulting in blurring or gloss or luster irregularities on the printed image. If a linear image composed of a succession of dots is printed on the receptive layer of a recording sheet with a pigment ink, then the surface of the printed linear image tends to crack.
It has been desired in the art to improve recording sheets by solving the contradictory problems with respect to water absorption and water resistance.